The steady growth in the use of popular consumer and industrial electronic devices, such as laptop computers, cellular phones, portable compact disc players, and desktop printers, is increasing industry demand for low ripple, power efficient, and high speed switching voltage regulators and power supplies. These types of products require power supplies which are inexpensive, light weight, and small.
Most currently available power supplies and voltage regulators use inductive or resistive components to regulate voltage output. Resistive components are inefficient, because they directly use energy as a means of providing a load with a specific voltage. Inductors store energy within a magnetic field, but are bulky, expensive, and suffer from winding resistance losses, eddy current losses, and hysteresis losses. Further, the use of inductors is not conducive to the manufacture of a power supply using modern lithographic methods.
Some power supplies use capacitors for the generation of DC voltage for low power applications, such as that disclosed in U.S. Pat. No. 5,414,614 to Fette et al., where banks of switched capacitors are used to step-up or step-down power. A digital controller is used to turn switches located within the capacitor network on and off in order to add in or exclude capacitors from the active network. However, since this power supply uses a highly complex array of capacitors and two closed loop controls, the response time to changes in power output ratio is suboptimal. Further, since the digital control disclosed in U.S. Pat. No. 5,414,614 uses a look-up table to configure the switched capacitor network, significant processing time is required to vary the voltage. These system limitations prevent the power supply from reacting effectively to an alternating or variable set-point for the generation of AC power. Finally, this power supply produces a certain amount of voltage ripple due to the particular configuration of the switched capacitors.
Accordingly, there is a need for a switched capacitor power supply which efficiently delivers a desired level of voltage, minimizes output voltage ripple, is constructed out of relatively few components for added reliability, provides energy efficiently with a minimum of energy loss in the form of joule heating, can react quickly to sudden load changes without inductive lag or voltage spikes created by sudden changes in current, and is suited for modern lithography for ease of implementation.